Dermot returned in the summer of 1167 a year after he had fled. A few Norman soldiers accompanied him. The rest arrived in three main groups:
1. The first group in May 1167
2. The second group in May 1170
3. The third group in September 1170
(Strongbow arrived with the third group.)
The first Norman invaders landed in Co. Wexford in 1169.
The 600 Norman foot-soldiers with their coats of armour and their deadly crossbows, were soon joined by Dermot MacMurragh and some of his followers. They marched on Wexford. After a short seige, the people of the town surrendered.
The Normans had better weapons and fighting methods than the Irish. O'Connor, the High King and O'Rourke of Breifne became alarmed at the success of the invaders and they marched with their armies into Leinster. A peace treaty was made between them -- MacMurragh was to be restored as King of Leinster on condition that the Normans return home. Dermot agreed to this, but had no intention of keeping his word.